Many processes are known to prepare bis-phenols. In some of these processes phenol is reacted with acetone to form bis-phenol-A. It is customary to then isolate the bis-phenol-A by crystallization, distillation or adduct crystallization. The concentrated residue contains many isomerizable components, such as o,p'-bis-phenol-A and other variations from bis-phenol-A. These components of the residue are usually isomerized in an acidic medium to the desired bis-phenol-A. The acidic medium includes inorganic acids such as hydrochloric acid and acidic cation exchange resins.
U.S. Pat. No. 3,221,061 discloses the preparation of bis-phenol-A and a subsequent "rearrangement" reaction conducted in the presence of a phenol saturated (mercapto alcohol modified) cation exchange resin.
U.S. Pat. No. 4,400,555 discloses a multi-step synthesis of bis-phenol-A in which acetone is injected in portions and an isomerization follows but the patent fails to illustrate the kind of catalyst in the isomerization zone.
U.S. Pat. No. 4,590,303 discloses a similar process in which the catalyst in the "rearrangement" reaction is a mercapto modified macroporous ion exchange resin and the acetone is injected into the "rearrangement" reactor. While the total conversion of acetone was increased, the percentage of undesired by-products also increased. However, from the data in the experiments in this patent, it can be seen that diverting a part of the acetone to the "rearrangement" reactor was adverse to isomerization since the selectivity to the desired bis-phenol-A became progressively worse. Thus, the desired isomerization was not demonstrated.
U.S. Pat. No. 4,375,567 discloses that both microreticular and macroreticular ion exchange resins in an unmodified form are used for isomerization. In this case, the microreticular resins were less effective for isomerization than the macroreticular resins.
There still exists a need to reduce or utilize the amount of undesirable by-products from the preparation of bis-phenols, e.g., bis-phenol-A from phenol and acetone or bis-phenolfluorene from phenol and 9-fluorenone. Obviously, the art has failed to find a method to react the two starting materials without the production of by-product isomers. Thus, there is still a need to more effectively convert these undesired isomers into the desired bis-phenol. The present invention addresses this problem and provides a new method to isomerize the undesired bis-phenols to the desired bis-phenol.